Electrical circuit overload protector of the thermally responsive bimetal element type



Oct. 20, 1970 u, CARTER ETAL j ELECTRICAL CIRCUIT OVERLOAD PROTECTOR OFTHE THERMALLY RESPONSIVE BIMETAL ELEMENT TYPE 4 sheets-shut 1 Filed llay13, 1968 Til I II... .|'.'.'1'|' II I Oct. 20, 1970 u, CARTER ETAL3,535,669

, ELECTRICAL CIRCUIT OVERLOAD PROTECTOR OF HE THERMALLY RESPONSIVEBIMETAL ELEMENT TYPE Filed May 13, 1968 7 4 Sheets-Sheet 2 i l! I I l Il l L J W04 I l I w I I Lim Oct. 20, 1970 u. F. CARTER ETAL ELECTRICALCIRCUIT OVERLOAD PROTECTOR OF THE THERMALLY RESPONSIVE BIMETAL ELEMENTTYPE 4 Sheets-Shet 3 Filed May 13, 1968 I I 19.8 Law an METAL (mm) I 5Ina/I zxn METAL (Buss) OCII. 20, 1970 T u E ETAL 3,535,669

ELECTRICAL CIRCUIT OVERLOAD PROTECTOR OF THE THERMALLY RESPONSIVE'BIMETAL ELEMENT TYPE Filed May 13, 1968 4 Sheets-Sheet 4 US. Cl.337-347 7 Claims ABSTRACT OF THE DISCLOSURE An electrical circuitoverload protective device of the thermally responsive bimetal typewhich can be selectively set for either automatic or manual reset modesof operation. Overload responsive units, for one or more circuitbranches employing stacks of bimetal discs as thermally responsiveelements, and are mounted within a housing on a common base. Eachoverload unit has an individual snap acting switch which opens inresponse to an overload condition as detected by the heat developed in aheater coil connected in the branch circuit which surrounds itsthermally responsive element. The switches of the overload units are allconnected in a single series circuit between terminals provided forconnection to a circuit to be controlled. In a manual trip-free mode ofoperation a pushbutton lever upon subsidence of all overload conditionsis depressed inwardly of the housing to aiford manual reset of themovable contact members of any switch tripped open by overload response.Alternately the reset lever may be latched in such depressed positionwherein the contact opening movement of the movable switch contactmembers is so limited that they will individually automatically resetupon subsidence of the overload condition in their respective branchcircuits. A modified form of ambient temperature compensated bimetallicdisc type of overload responsive unit is pro- 'vided for use wherein thedevice will be subjected to high or widely varying ambient temperatureconditions.

Features of the invention described in this application are disclosedand claimed in the copending Uriel F. Carter and Edward A. Mallonenapplication Ser. No. 729,496, filed May 13, 1968 and assigned to theassignee of this application.

This invention relates to an improved overload protective device of thethermally responsive, bimetal element type.

A primary object of the invention is to provide a protective device ofthe aforementioned type employing bimetal discs in a special stackedrelation as the thermally responsive element in each of one or moreoverload units.

Another object is to provide in each overload unit a separatesnap-action electric switch for individualized control by its associatedthermally responsive element of the aforementioned type.

A further object is to provide a protective device of the foregoing typewhere the aforementioned switches of the individual overload units areelectrically connected in a single series circuit so that the latterwill be interrupted upon opening of any switch unit in response to anoverload condition to which its associated thermally responsive elementmay be subjected.

Still another object is to provide an overload protective device of theaforementioned type which can be selectively set so that reset ortripped switches of the United States Patent 3,535,669 Patented Oct. 20,1970 overload unit will automatically reset, or alternatively requiremanual operation of a reset lever to effect reset of the switches uponsubsidence of the overload conditions in protected circuit branches.

An additional object afforded by the overload device is trip-free actionof the switches of the respective overload elements in the event theoverload condition has not subsided when the reset lever is manuallyoperated.

A still further object is to provide a modified form of ambienttemperature compensated overload responsive element of theaforementioned bimetal disc type which can be used interchangeably forthe overload device for those aforementioned.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawings illustrate preferred embodiments of theinvention which will now be described in detail it being understood thatthe embodiments disclosed are susceptible of modification in respect ofdetails without departing from the scope of the appended claims.

BRIEF DESCRIPTION OF'DHE DRAWINGS FIG. 1 is a top plan view of anoverload circuit protector switch incorporating the invention;

FIG. 2 is a front elevational view of the switch;

FIG. 3 is a left end elevational view of the switch with portions of thehousing broken away;

FIG. 4 is a view similar to FIG. 3 but showing the switch in anotheroperating mode;

FIG. 5 is a top plan view of the inside of the housing base showing theoverload responsive switch mechamsm;

FIG. 6 is a fragmentary cross sectional view taken generally along theline 66 of FIG. 1 showing an overload responsive element;

FIG. 7 is a view similar to FIG. 6 but showing a modified form ofoverload responsive element;

FIG. 8 is a view in.cross section to greatly enlarged scale of a portionof a stack of bimetal disc elements shown in FIGS. 6 and 7;

FIG. 9 is a more or less schematic representation of the overloadelement depicted in FIG. 6;

FIG. 10 is a view like FIG. 9, but showing the overload device inanother operating condition;

FIG. 11 is a view like FIG. 5 but 'with the overload responsive andswitch elements removed; and

FIG. 12 is an isometric view of a switch drive lever and movable membershown in FIGS. 5, 6 and 7.

DETAILED DESCRIPTION Referring to FIGS. 1 to 3, they show a circuitprotector switch having a metal mounting plate 10, a unitary insulatinghousing 12 to which plate 10 is attached, and an insulating bottom coverand base member 14. The switch has a reset button 16 mounted on the endportion of a metal lever 18 which is reciprocably movable in a guidepassage 12a formed in housing 12.

The top opening recesses 20' are provided on housing 12. Intermediatepartition portions 22, 24, 26 and right-hand end wall 28 of housing 12provide electrical barriers between the recesses. Spaced apart pairs ofcombination wire terminal and overload heater mounting plates 30 aresecured in place in each of the recesses by screws 32 which take intothreaded recesses. One of each pair of plates 30 located at the rear ismounted at a higher level than the plate at the front. The center recessbetween partitions 24 and 26 is at a higher elevation to provideincreased electrical and heat clearance between each adjacent sets ofrecesses and to provide for clearance for the interfit of a terminalmounting member 98.

As thus far described, the housing 12 and elements mounted thereon areexactly the same as a counterpart housing shown and described in theCarter et al. application, Ser. No. 699,270, filed Jan. 19, 1968 and nowPat. No. 3,478,292, and assigned to the assignee of the presentapplication. Housing 12 was designed to be interchangeably used in bothtyes of overload protector switches.

Each of the aforementioned top opening recesses in housing 12 hasmounted therein between the spaced plates 30, a plate 34 to which isfastened a metal cylindrical tube 36 which has an anodized insulatingexterior surface. The plates 34 are secured in place by screws 38. Aswill hereinafter be more fully explained, bimetal disc overload elementsare centered without appreciable peripheral clearance in each of thetubes 36, and as shown in the left-hand recess between partitions 22 and24, a helical heater coil 40 is positioned around and in contact witheach of the tubes 36 and secured to the upper and lower terminal platesby screws 42.

The terminal plates 30 have outward and slightly downwardly projectingtabs 30a to which are secured wire retaining members 44 by screws 46. Inactual service, the other two recesses would also be fitted with heatercoils 40, the same having been omitted in FIGS. 1 and 2 to clarifyconstruction details of the plates 34 and tubes 36.

With each pair of terminals 30 wired in series in branches of athree-phase A.C. circuit it will be apparent that the heater coils 40will be subjected to the load current in their respective branches. Heatgenerated by such current flow will transfer by conduction to the tubes36, and as will hereinafter be explained, causes movement of the bimetaldiscs of the overload elements.

As shown in FIGS. 5, 6 and 11, the overload responsive elements andswitches controlled thereby for each of the three branches are mountedon the inside of base 14. As best seen in FIGS. and 6, each overloadresponsive element comprises a support bracket 48, a rectilinear movablerod 50, a stack of bimetal discs or washers 52, a loading spring 54, aspring gland 56, an adjusting pin 58 and adjusting screw 60. A flangedcylindrical insulating member 62 seats against the flanged end portion50a of rod 50 and provides a spindle on which the stack of discs 52 aremounted. A cylindrical insulating spacer 64 abuts at its upper endagainst the lowermost bimetallic washer and has the lower end portion ofspindle 62 projecting into its bore.

The lower end of spacer 64 seats against the upper end of adjustingscrew 60 which is centrally bored to accommodate rod 50, and exteriorlythreaded to be adjustable in the complementally threaded insert 66molded in place in the upper arm 48a of bracket 48. Adjusting screw 60has a laterally and upwardly extending arm 60a which extends through anarcuate slot 34a formed in cover plate 34. As will hereinafter beexplained, lever 60a within the limits of slot 34a affords a certainrange of adjustment for controlling the compression loading of the stackof discs 52.

Adjusting pin 58 has a cylindrical flanged end portion 580:, anintermediate portion 58b which is rectangular in transverse crosssection and an upper cylindrical end portion 580 of reduced diameter.The upper end portion 580 is internally threaded and the lower endportion of rod 50 is threadedly engaged therein. Also the upper endportion 580 projects into an opening 56a which extends from the lowerend of gland 56 to the bottom of the spring receiving recess 56b thatopens to the upper end of the gland. Loading spring 54 is of the coiledcompression type and seats at its upper end in a shallow recess 48bformed in the lower surface of arm 48a of bracket 48 and at its lowerend against the bottom of recess 56b in gland 56.

As shown in greatly enlarged cross section in FIG. 8, the bimetal discs52 comprise two metal layers; layer 52a having a relatively highcoeflicient of thermal expansion and the other 52b having a relativelylow coeflicient of thermal expansion. In plan view the discs 52 areannular, and as shown in FIG. 8, they are convexly warped in transversecross sectional form similar to that found in Belleville washers. Theyare stacked on the spindle portion of the guide 62 in the arrangementshown in FIG. 8 with one pair abutting along respective concaved edges,and an adjacent pair abutting on respective opposed convexed surfaces,etc., in a repeating alternate series. At ambient or room temperaturethe distance between hottoms of concaved surfaces on alternate pairswill be some distance X.

As the temperature of the discs 52 increase they will individuallyflatten and each of the distances X will decrease with increasingtemperature. Consequently, the total height of the stack of discs 52will decrease as a function of the sum of the individual decrease in X,between alternate pairs of discs in the stack. If the temperature of thediscs 52 thereafter decreases the individual distance X increases as theindividual discs in the stack return to their ambient temperature warpedor dished shape in cross section depicted in FIG. 8.

The foregoing arrangement of the discs 52, in affording decrease inindividual warpage with increase in temperatiire is an advantage. As thestresses between the discs decrease with rise in temperature, subjectionto thermal shock temperature rises which can occur during highelectrical overload conditions will prevent the elastic limit of thediscs from being exceeded. Accordingly, repeatability of change in totalstack height and hence the force developed by the discs 52 for a giventemperature change is considerably enhanced.

The lower end of glaid 56 bears against arcuate protrusions 68a formedon each of the arms 68b of a switch drive lever 68. Drive lever 68 isprovided with a central rectangular opening 680 which accommodates therectangular portion 58a of adjusting pin 58. The arms 68b which aredisposed on opposite sides of opening 68c also have arcuate protrusions68d which bear against the upper surface of the end portions 58a of pin58. Drive lever 68 has upstanding end portions 68a and 68 which areprovided with V-shaped notches 68g and 6811, respectively. Portion 68aengages within its notch 68g the inner edge of an opening of a movable,flat leaf switch member 70 which carries a contact 72 (see FIGS. 6 and12). A C- shaped snap spring 74 seats along one edge in the notch 68h oflever 68 and has attached within, a slot 7411 with outer arms 70a and70b and intermediate contact carrymg portion 700 of member 70.

The opposite end portion 70d of member 70 is sandwiched together withportion 76a of current conductor 76 between an upstanding boss 14bformed on the inside surface of boss 14 and the lower surface of themounting pad 480 of bracket 48. As best shown in FIG. 5, screws 78 whichpenetrate alined openings in pad 480, portion 70d of member 70 andportion 76a of conductor 76 secure the member 70 and conductor 76 inelectrical contact in place on base 14.

As best shown in FIGS. 6 and '11, contact 72 through movement of member70 is adapted to engage with a stationary contact 80 secured to theportion 82a of a current conductor '82 which is in turn secured to aboss 14c on base 14 by a screw 84.

Switch member 70 together with snap spring 74 and drive lever provide asnap action type of electrical switch such as that disclosed and claimedin Pat. No. 3,207,868. Reference should be made to that patent fordetailed information on the formation and arrangement by switch member70 and snap spring 74.

Reference will now be made to FIGS. 9 and 10, to provide anunderstanding how each of the overload responsive devices and snapswitches function under normal and overload electrical conditions. Therepresentations in FIGS. 9 and 10 are simplified showings with certainparts of the overload devices hereinbefore described deleted. Numeralsof like parts have been designated with additional prime postscripts.The overload device and switch as shown in FIG. 9 are in positionsassumed under non-overload conditions. The bimetal discs 52' areenlarged and shown with exaggerated curvature for purposes ofillustration.

It will be seen that spring 54' urges gland 56 downwardly against switchdrive lever 68' and tends to cause the left end of snap spring 74' tomove downward, and hence tends to toggle member 70' upwardly todisengage contact 72 from contact 80'. However, a balancing upward forceexerted on drive lever 68' by adjusting pin 58' due to the counter forceaction of the bimetal discs 52' acting through rod 50' holds the snapswitch in the contact engaged position depicted in FIG. 9.

Now assume that a current overload condition occurs and persists. Thusthe heat transferred by conduction from the current carrying coil 40 tothe discs 52' will cause them to flatten in a direction decreasing thedegree of their individual convexed curvature. Thus the distance Y inFIG. 9 between the upper flanged end of rod 50 and spacer 64' willdecrease to the distance depicted in FIG. 10 and rod 50 consequentlymoves downwardly. The force exerted by spring 54 then causes gland 56 tomove downwardly and hence move drive lever 68' downwardly. When the leftend of snap spring 74 is moved across the plane of leaf member 7 0',snap action toggling of the latter member in the upward direction occursto disengage contact 72' from stationary contact 80' as depicted in FIG.10. Drive lever 68' during such snap movement pivotally moves by virtueof its protrusions 68a and 68d rocking on the upper surface of portion58a and the lower end of the spring gland 56. In the first positionmember 70' bears against a stop-reset bar 86'.

It may be assumed that when the overload condition has subsided, discs52 will cool and hence assume their normal or ambient temperaturecurvature condition. Thus the distance Z depicted in FIG. 10 willincrease and rod 50 will be moved upwardly to correspondingly move drivelever 68 upward. With stop-reset bar 86' set in the rotarypositiondepicted in FIGS. 9 and 10, the apex of notch 68h will not move upwardlybeyond the plane of member 70' by the time rod 50 and drive lever 68'reach their respective normal, or non-overload position depicted in FIG.9. In other words, the overload responsive switch will not automaticallyreset upon subsidence of the overload condition, and member 70' mustthen be manually reset (moved downwardly across the apex of notch 68h)to return it to the circuit closed position of FIG. 9. This willhereinafter be more fully explained in conjunction with FIGS. 4 and 5.

If stop-reset bar 86 is instead set at the rotary pos tion depicted forbar 86 in FIG. '6 when the aforedescnbed overload condition occurs,member 70' upon snap upward movement will assume a switch-open positionintermediate those depicted in FIGS. 9 and 10. Hence, upon subsequentsubsidence of the overload condition the apex of notch 68h will moveacross the plane of member 70' to cause snap toggling of the latter tothe circuit closed position shown in FIG. 9. In other words, the switchwill automatically reset upon return of the overload responsive deviceto normal or non-overload conditions. This action will also be morefully described in conjunction with FIGS. 4 and 5.

Now referring to FIG. 11, it will be seen that con ductor 82 has anintegral portion 82b like portion 76a of conductor 76. A secondconductor 82 is also secured on boss 14c on base 14 to the right of thefirst mentioned conductor 82. A third conductor 88 is secured to boss140 by a screw 90 and has a stationary contact 92 secured thereto.Conductor 76 has an integral L-shaped portion 76b which seats within acomplementally formed recess 14d in member 14 and a portion 76c whichextends upwardly at a right angle to aflford electrical connectionbetween portion 76b and a terminal end portion 76d. Conductor 88 has aportion 88a lying in a shallow recess in base member 14 that connectswith a portion 88b which is bent upward at right angles and thenlaterally toward the left as viewed in FIG. 11. Portion 88b connectswith a terminal end portion 88c like portion 760 of conductor 76.

As best shown in FIGS. 2, 5 and 11, terminal members 94 and 96 aresecured together with terminal portions 76d and 880, respectively, to alower surface of side boss portions 98a and 98b of an insulatingterminal mounting member 98 which has an intermediate barrier portion98c. As best seen in FIGS. 2 and 5, terminals 94 and 96 have outwardlyand slightly downwardly depending tabs 94a and 96a to which are securedby screws 100, wire retaining members 102 of a form similar to theaforementioned members 44.

Now referring to FIGS. 5 and 11, it will be seen that the overloadswitch device comprises three overload switch devices. With theirrespective switches closed, it will be apparent that current Will becompleted from terminal member 94 to 96. Thus with terminals 94 and 96appropriately connected in the energizing circuit of an electromagneticcontactor or relay (not shown) such circuit will be maintained when nooverload condition exists in any of the branches of the polyphasecircuit in which the heater coils 40 associated with the respectiveoverload devices are connected.

In the event an overload occurs in any such branch circuit sufficient tocause opening of its associated overload responsive switch the circuitwill, of course, be opened between terminals 94 and 96, thereby openingthe circuit to any electromagnet or other circuit that may be connectedthereto.

Referring to FIGS. 3, 4 and 5, it will be seen that stop-reset bar 86 isjournaled for rotation on cylindrical end portions 86a in the bearingbrackets 14 and 14g formed integrally with member 14. Immediatelyadjacent bearing 14 in FIG. 5, rod 86 is provided with an arm 86b, andbetween the latter and its opposite end portion 8611 it has a portion86c with the cross sectional form best shown in FIGS. 6, 9 and 10.

The arm 86b of rod 86 is disposed within the opening 104a of aninsulating member 104 which is molded about and is an extension of resetlever 18. A coiled compression spring 106 seats at one end within arecess 14h formed in base 14 and at its other end fits about a shortcylindrical boss 104b formed on member 104. Spring 106 biases member 104and lever 18 upwardly to normally assume the position depicted in FIG.4. In moving to that position the lower lip portion 104c at the entranceof opening 104a in member 104 engages arm 86b and rotates it clockwiseto the position depicted in FIG. 4. In this latter position the portion86c will be rotated to assume the position depicted for rod 86 in FIGS.9 and 10.

If reset lever 18 is moved inwardly of housing 12 to the positiondepicted in FIG. 3, the upper lip portion 104d of member 104 engages arm86b of rod 86 and rotates the latter to the position depicted in FIG. 3wherein the portion 86c then assumes the rotary position depicted inFIG. 6. It will be seen that in this last mentioned rotary position forthe portion 86c the clearance distance between the free ends of themovable switch member 70 is considerably less than in positions depictedfor rod 86' in FIGS. 9 and 10.

If with the rod 86 in the rotary position depicted in FIG. 6, anoverload occurs, the free end of any switch member 70 which moves tocontact disengaging position will engage the rod 86 and thereby limitits movement. With the contact opening movement of any member 70 solimited, any tripped switch will automatically reset upon subsidence ofthe overload condition as aforedescribed. It will also be understoodthat after responding to an overload condition, a switch member 70 ismoved to an open position depicted for member 70' in FIG. 10 that 7subsequent rotation of rod 86 to the position shown in FIG. 6 followingsubsidence of the overload condition will cause it to engage the end of.the member 70' and move it downwardly sufficiently so that snap spring74 will then toggle the same to the contact engaged position shown inFIGS. 6 and 9.

When lever 18 is moved to its inward extreme position shown in FIG. 3,it can be retained latched in that position by moving a lever 108 intoengagement in a notch 18a formed in lever 18. Thus rod 86 will beretained in the rotary position wherein its portion 86c assumes theposition depicted in FIG. 6. Accordingly, the overload device will beset in its automatic reset mode, and upon subsidence of overload in allbranches circuit completion between terminals 94 and 96 will beautomatically restored.

Lever 108 is provided with an elongated opening and a screw 110penetrates such opening and takes into a threaded recess a housing 12.When lever 108 is engaged within the notch 18a of lever 18 tightening ofscrew 110 insures retention of reset lever in the automatic reset mode.Of course, when lever 108 is out of engagement with lever 18 it can alsobe held in that position by tightening of screw 110.

The temperature trip point of any of the aforedescribed overloadresponsive switches is determined by the adjustment of adjusting pin 58on the threaded end of rod 50. Turning pin 58 further on to rod 50 will,through its bearing on drive lever 68, move the latter upwardly acorresponding amount. Drive lever 68 because it bears against the lowerend of gland 56 will move the latter upwardly and spring 54 will becorrespondingly compressed. Spring 54 then exerts increased forcedownwardly on gland 56, drives lever 68, pin 58 and rod 50. Thus discs52 will be caused to be compressed, and their stack height reduced.Accordingly, the upward force exerted on rod 50 by the stack of discswill then counterbalance the inward force of spring 59 acting downwardlyon drive lever 68 at its new upper position.

It will be apparent that with drive lever 68 moved upwardly that theapex of its notch 68h will be moved upwardly a corresponding amountabove the plane of movable contact member 70. Hence lever 68 will haveto be moved downwardly a greater distance before the apex of notch 68hpasses the plane of member 70 at which point snap-action toggling of thelatter to contact opening position occurs. Accordingly, theaforedescribed change in adjustment of pin 58 results in an increase ofthe trip point temperature. It will be apparent from the foregoing thatif adjusting pin 58 is backed farther down from an initial position onrod 50, that the trip point temperature will be decreased.

Screw 60 affords another more limited adjustment of the trip pointtemperature of each overload device. If lever 60a is turnedcounterclockwise in slot 34a in plate 34, as viewed in FIG. 1, screw 60will advance upwardly in insert 66 thereby moving spacers 62 and 64upwardly which results in increased compression and hence decrease inthe height of the stack of discs 52. As a consequence of this drivelever 68 is moved upwardly to a new ambient temperature position.Conversely, if lever 60a is rotated clockwise in slot 34a the height ofthe stack of discs 52 will decrease resulting in a correspondinglowering of the ambient temperature position of drive lever 68. Thearcuate length of the slot 34a determines the range of change in trippoint temperature that can be effected by adjustment of the screw 60.

Normally the basic trip point temperature is determined after assemblyof the overload device by adjustments of pin 58- to afford a trip" pointtemperature which is some specified value above normal ambienttemperature. Then with selection of a heater coil most appropriate forthe particular load conditions, screw 60 permits a limited range changeto partially compensate for the fixed increments existing between aheater coil of a given rating and those available which are immediatelyabove or below it in rating tables.

FIG. 7 shows a modified form of ambient temperature compensated overloadresponsive switch unit which can be used in place of thoseaforedescribed. In this modified form the loading spring 54 is deletedand a stack of bimetal discs 112 together with a spacer 114 inserted inits place. The discs 112 are the same in form as the discs 52, butsomewhat greater in outer diameters, and warped depth at the sameambient temperatures. They are also stacked in the same arrangement asshown for discs 52 in FIG. 8.

It will be apparent that if the modified overload re sponsive switchunits are subjected to ambient temperature conditions which varyrelatively widely, that change in forces developed by the discs 52 withtemperature will be oifset by a corresponding change in forces developedby the discs 112. Consequently, the distance of the notch 68h of drivelever 68 above the plane member 70 (in contact closed position) will notchange appreciably as the ambient temperature varies. Thus the trippoint temperature of the compensated overload devices will not beappreciably affected by ambient temperature changes that may beencountered in certain conditions of mounting and housing of theoverload devices.

The use of the ambient temperatures compensated overload responsiveunits is desirable when the overload protection switches are inside ofenclosures which are subject to internal generation of heat by otherequipment mounted therein, or to external heat such as by the sun orother heat radiating sources.

What is claimed is:

1. A thermally responsive overload switch comprising, in combination:

an electric switch having an operating lever movable in oppositedirections to eifect opening and reclosing of switch contacts, and

a thermally responsive switch operating mechanism comprising:

a stationary abutment,

a guide member in engagement with said operating lever,

a coil compression spring disposed between said guide member and saidabutment,

a reciprocally movable member,

an adjusting member threaded on said reciprocally movable member andengaging said operating lever in opposed relation to said guide member,a plurality of stacked dished annular bimetal discs disposed about saidreciprocally movable member(s), and bearing against the latter and saidabutment,

said discs under ambient temperature conditions biasing saidreciprocally movable member in a direction opposing movement of saidoperating lever in said contact opening direction.

2. The combination according to claim 1, wherein said switch operatingmechanism further includes a second adjusting member threaded into saidabutment and bearing against stacked washers, said second adjustablemember being adjustable over a limited range to increase or decrease thestatic compression between said bimetal discs.

3. A thermally responsive overload switch comprising in combination:

an electric switch having an operating lever movable in oppositedirections to eifect opening and reclosing of switch contacts, and athermally responsive switch operating mechanism comprising:

a reciprocally movable member, an adjusting member threaded on one endof said reciprocally movable member and engaging said operating lever, astationary abutment, a guide member in engagement with said switch oroperating lever,

a plurality of dished, annular bimetal discs disposed about saidreciprocally movable member and bearing against the other end of thelatter and one side of said abutment,

a second stack of dished annular bimetal discs disposed about saidreciprocally movable member and bearing against the other side of saidabutment and said guide member,

said two stacks of bimetal discs under ambient temperature conditionsoppositely biasing said reciprocally movable member and said guidemember so that said switch operating lever is maintained in said contactclosed position, and

said first mentioned stack of bimetal discs under overload temperatureconditions transversely flattening to a degree such that the biasexerted by said reciprocally movable member on said switch operatinglever is so reduecd that the latter can move to its contact openingposition.

4. In an electric overload circuit protector, in combination:

a housing having a plurality of recesses in the upper side thereof withinsulating barriers therebetween for electrically isolating saidrecesses from each other,

at least one thermally responsive switch unit each having an electricswitch with a movable contact element mounted interiorly of saidhousing, a constricted stack of dished, annular bimetal discs disposedwithin one of said recesses, and having means within said housingresponsive to flattening of said discs under high temperatures tooperate the movable contact element of said switch to open circuitcondition,

means including a pair of terminals mounted exteriorly of said housingand conductors within said housing interconnecting the switches of allthe aforementioned switches in series between said terminals, electricheater coils mounted concentrically about each stack of bimetal discsand when connected in series in different branches of an electriccircuit subjecting their respective associated stacks of bimetal discsto temperatures which are a function of the currents in such branches.

5. The combination according to claim 4, together with means including areciprocally lever extending exteriorly of said housing which isdepressible to eifect reset of any tripped overload responsive switchupon subsidence of overload conditions, said lever being alternativelylatchable in depressed position to limit the degree of switch openingmovement of the movable contact element any overload tripped switch sothat they will individually automatically reset upon return of theirstacks of bimetal discs to ambient temperature states.

6. The combination according to claim 5, wherein said means includingsaid reciproca ly lever further includes a member mounted for rotationwithin said housing and having a portion overlying the paths of movementof the movable contact elements of all the aforementioned switches, saidreciprocally lever engaging said rotatable member and when moved to itsdepressed position rotating said rotatable member to a given positionwherein the contact carrying members of any tripped switches are movedan amount insuring their reset when the bimetal discs return to ambienttemperature states.

7. The combination according to claim 5, wherein said overload circuitprotector includes at least two thermally responsive switch units,wherein said bimetal discs in each stack are mounted so that alternatepairs of discs have their concaved surfaces opposing each other and thelayer of metal on such concaved surfaces has the higher coeffi: cient ofthermal expansion, and wherein said housing is in two parts with a firsthollow part having the aforementioned recesses formed therein and asecond bottom cover part having the thermally responsive switch unitsmounted thereon.

References Cited UNITED STATES PATENTS 3,315,054 4/1967 Langley 337-72XR 3,172,971 3/1965 Roeser. 3,140,370 7/1964 Harper 337-112 XR 3,044,2957/ 1962 Shivers 73-3635 XR GEORGE HARRIS, Primary Examiner D. M. MORGAN,Assistant Examiner U.S. Cl. X.R. 337348, 354

